Methods for applying particulate coating materials to continuous-length bundles of fibers (i.e., tow and roving) are well known in the art. Typical are the techniques described in the following U.S. patents:
Swann U.S. Pat. No. 2,730,455 provides a method for coating threads or roving in which a high-potential electrostatic field is employed to spread the fibers prior to coating.
In the method of Stranch et al, U.S. Pat. No. 3,586,560, the filaments of a strand are spread to a parallel relationship, by passage under tension across a surface of a rod-like member, preliminary to coating in a fluidized bed; particle adherence may be promoted by charging either the strand or the powder particles.
U.S. Pat. No. 3,354,013, to Terrell et al, discloses a method for applying particulate additives to a band of continuous filament tow in a fluidized bed, the additive being applied to both sides of the band during passage about rolls disposed in the bed.
The apparatus taught by Lamanche et al, U.S. Pat. No. 3,703,396, serves to separate individual fibers of a strand, using air currents or electrostatic charges, to effect coating with a resinous material, which may also be electrostatically charged.
In the method described in Spencer U.S. Pat. No. 3,673,027, the filaments of a strand to be coated are spread, and subjected to back-tension, as they enter a fluidized bed of particulate coating material.
Mayer, Jr., et al, U.S. Pat. No. 3,707,024, provides a method for electrostatically bulking and impregnating yarns.
In accordance with Price, U.S. Pat. No. 3,742,106, glass rovings are spread, and separated into bundles of filaments, as by passage over threaded bars, during powder impregnation in a fluidized bed.
Crossbars are utilized in Brown et al, U.S. Pat. No. 3,817,211, as electrodes for electrostatically charging the individual filaments of a strand to open it, as it passes thereabout under tension, and to promote impregnation by electrostatically charged particles.
In accordance with Gray et al, U.S. Pat. No. 4,098,927, glass roving is drawn under and over a series of bars to separate it into a number of bundles of filaments, to thereby promote entrainment of resin powder from a fluidized bed.
McAliley, U.S. Pat. No. 4,714,642, discloses the random decollimation of multifilamentary tow, so as to create a multitude of interstices between adjacent filaments for the receipt and retention of matrix-forming resin.
U.S. Pat. Nos. 5,094,883 and 5,171,630, to Muzzy et al, are directed to a "multiply towpreg," produced by powder coating (e.g., in an electrostatic fluidized bed) of filaments spread in a generally columnated manner and maintained under tension.
Despite such prior art, a substantial need exists for means by which particulate materials can be applied to a continuous length workpiece, comprised of a bundle of filaments, or fibers, in a manner that is less complicated, very efficient, and that readily produces a uniform distribution, and selectively controlled loading, of the coating material in the workpiece.